Renal oncocytosis: a clinicopathological and cytogenetic study of 42 tumours occurring in 11 patients.

Renal oncocytosis is a rare pathological condition characterised by the presence of multiple oncocytic tumours with a spectrum of histological features ranging from renal oncocytoma, hybrid oncocytic tumour and rarely chromophobe renal cell carcinoma, sometimes overlapping. Here we retrospectively analysed histological, immunohistochemical (IHC), and cytogenetic features of 42 lesions in 11 patients with renal oncocytosis, not associated with Birt-Hogg-Dubé syndrome. The histology of all the lesions was blindly reviewed by three dedicated genitourinary pathologists. IHC for cytokeratin 7 (CK7) and fluorescence in situ hybridisation (FISH) for copy number variation of chromosomes 1, 6, 7 and 17 were performed in all 42 nodules. Among the 42 lesions 36 (85.7%) were histologically renal oncocytomas, two (4.76%) 'hybrid oncocytic tumours' (HOT), one (2.4%) clear cell renal cell carcinoma (ccRCC), one (2.4%) papillary renal cell carcinoma (pRCC), one typical angiomyolipoma (2.4%), and one mixed epithelial/stromal tumour of the kidney (2.4%). FISH analysis confirmed the histological diagnosis of all the lesions. We show that most patients with renal oncocytosis harbour benign or low malignant potential tumours that can be treated conservatively.